This invention relates to valve controls for internal combustion engines and, more particularly, to controls providing variable valve lift.
Internal combustion engines employ intake and exhaust valve mechanisms to control the fuel/air mixture within the engine cylinder. The intake valve controls the incoming charge of fuel and air, and the exhaust valve controls the outgoing products of combustion. The engine operates on a four cycle or stroke principle consisting of intake, compression, power, and exhaust. The intake valve is open for at least a majority of the intake stroke and the exhaust valve is open for at least a majority of the exhaust stroke. Some engines operate with an overlap between the intake and exhaust valves during a change from the intake stroke to the exhaust stroke.
Most engines operate with a stoichiometric air/fuel ratio of approximately 15:1 which will generally support substantially complete combustion of the air/fuel mixture. The combustion of the air/fuel mixture provides the power required to drive the piston in the cylinder during the power stroke. There are valve control systems that control at least the lift or opening amount of the intake valve. The more successful of these systems employ multiple cams or multiple cam followers. The operable portion of these systems is selectively connected with the cam shaft or follower shaft by a clutching mechanism. Other systems have proposed a laterally moveable cam follower to change the valve lift motion. These systems employ complex mechanisms to achieve the desired result of variable valve opening.
One valve control mechanism, described in U.S. Pat. No. 3,422,803 issued Jan. 21, 1969, utilizes a pushrod, a rocker arm, and an adjustable pivot for controlling the valve lift of an intake valve. The rocker arm is a floating member that is held in place by the pushrod, adjustable pivot and the valve stem. The rocker arm does not have a firm connection with any of these members and therefore relies on spring loads and frictional engagement to remain in place. The contact between the adjustable pivot and the rocker arm is a cam-type contact that is positioned between the pushrod contact and the valve stem contact. Each of the contact points has a frictional contact that adds heat to the system and thereby presents a disadvantage by reducing the overall efficiency of the engine.
It is an object of the present invention to provide an improved valve lift control in an internal combustion engine.
In one aspect of the present invention, a rocker arm is pinned for pivotal movement to the stem of the valve. In another aspect of the present invention, the adjustable pivot and the cam are on opposite sides of the pivot joint at the valve stem. In yet another aspect of the present invention, the contact between the adjustable pivot and the rocker arm is a rolling type contact, as is the contact between the cam and the rocker arm.